This invention relates to metal-air cells and, more particularly, to electrochemical power generating systems using metal-air cells.
Metal-air cell batteries generally have several serially connected metal-air cells. Each cell has an anode made of a reactive metal such as aluminum or magnesium and an air cathode spaced from the anode. A suitable electrolyte, such as an aqueous solution of KOH, NaOH or NaCl, electrochemically couples the anode and cathode to produce an electrical potential and supply current to an electrical load. During the electrochemical reaction, the anode is consumed. When the anodes are consumed, the battery must be refueled with new anodes and fresh electrolyte. Such refueling generally requires draining of spent electrolyte from the battery, adding new metal anodes one-by-one, and replenishing the electrolyte. The refueling operation in prior art metal-air batteries is time consuming and usually results in the machine or device powered by the battery being inoperative for an extended period during refueling.
Another problem with prior metal-air cell batteries is that during anode consumption the distance between the anode and cathode increases causing a decrease in voltage, power output, and efficiency of the battery.
Another problem is degradation of the electrolyte solution. As the reaction in the cell proceeds, reaction products build up in the electrolyte solution, and concentration of the electrolyte increases, both of which cause a decrease in performance of the cell.
Another problem with prior metal-air cell batteries is the length of time it takes for the battery to become fully operational, i.e., to deliver full power. The temperature of the electrolyte circulating through the battery must be relatively high (e.g., 150.degree. F.) before the battery can fully energize the load. A metal-air cell cannot deliver much power at low temperatures and, consequently cannot generate much heat. Thus, if the electrolyte is initially cold, it typically takes several minutes to heat the circulating electrolyte to a sufficient operating temperature. Such a warm-up time is often a nuisance to the user and renders such metal-air cell batteries impractical for many applications. Moreover, when the cell is disconnected from its electrical load, the anode continues to be consumed at a low rate and thereby reduces the operating life of the cell.